Hippocampus casscsio, Zhang, Yan-Hong, Qin, Geng, Wang, Xin & Lin, Qiang, 2016

Zhang, Yan-Hong, Qin, Geng, Wang, Xin & Lin, Qiang, 2016, A new species of seahorse (Teleostei: Syngnathidae) from the South China Sea, Zootaxa 4170 (2), pp. 384-392 : 385-389

Hippocampus casscsio sp. nov.

Beibu Bay seahorse

Figs 1 , 2 a, 3, 4, Table 1

Holotype. SCSMBC007414 (SL 90.5 mm, male), Beihai , Beibu Bay, China (approximately 21°20’ N, 109°02’ E), depth 15 m, collected by Qiang Lin, 12 May 2012 . Paratypes: SCSMBC007415, 15 specimens (122.5 mm, female; 111.0 mm female; 132.0 mm, female; 104 mm, male; 100.5 mm, female; 106.5 mm, male; 88.0 mm, female; 126.5 mm, male; 129.0 mm, male; 133.0 mm, male; 121.5 mm, female; 117.0 mm, female; 102.5 mm, female; 118.0 mm, male; 120.5 mm, male), collection data as for holotype.

Diagnosis. Hippocampus casscsio sp. nov. is diagnosed from other seahorse species by the combination of the high number of tail rings (34–37), 15 pectoral-fin rays, 16 dorsal-fin rays (dorsal fins covering 2 trunk rings and 2 tail rings), a rounded nuchal plate without a raised coronet, the snout length approximately 30% in HL, one eye spine, two cheek spines, the tail length approximately 60% in SL, the plain dark brown body color, and male owning a fully enclosed brood pouch with a small opening for the incubation of eggs.

Description. In addition to the characteristics given in the diagnosis (holotype, paratype range in brackets): HL 15.8% (11.6–17.6%), TrL 28.2% (23.7–35.1%), TaL 56.0% (48.5–62.8%) in SL; SnL 30.5% (25.0–43.3%) in HL; TrR 10 (10–11), surface of TrR1, TrR4, TrR7 and TrR2 expanded laterally (but without spines); dorsal fin base starting immediately posterior to 9th trunk ring and ending immediately posterior to 2th tail ring (covering 2+2 rings); pectoral fin-base raised; DF 16; pectoral fin-base raised; PF 15; anal fin visible with 4 rays; first tail ring quadrangular; TaR 35 (34–37).

Body ornamentation: a prominent rounded spine above each eye, on midline of snout between eyes, and on either side of head below coronet; shoulder spine at base of pectoral fin; cheek spine.

Sexual dimorphism: males with closed brood pouch and slight keel anterior to dorsal fin base; greatly extended spines on inferior ridge on TaR 1–6th surrounding the brood pouch; females with slightly raised, circular genital opening; Males slightly larger SL, 116.0 mm (90.5–133.0 mm) compared to females 111.9 mm (88–132 mm).

Compared to other similar species, Hippocampus casscsio sp. nov. is notable for its short snout length and long tail length. Significant differences between H. casscsio sp. nov. and H. kuda specimens were detected in SnL/HL and TaL/SL ratios ( Table 1 ). H. kuda also had a low-medium, rounded coronet with a cup-like depression on the top, which differed from the new species ( Fig. 2 a). H. casscsio sp. nov. is much larger than that of H. mohnikei ( Fig. 2 a).

Principal component analysis showed that 11 metric and meristic characters integrated into 2 principal components and cumulatively contributed to 95.5% of total variance ( Table 2 ). As the component matrix shows, the SL and BH had the highest factor loading in the first principal component, and the TrR had the highest factor loading in the second principal component. Standardized morphological data of all individuals were plugged into PCA function to calculate the score of the two factors. The score of the principal components is presented on Figure 2 b. Ordination of the data using PCA showed no overlap among the three species seahorses included in this analysis.

Sample size for each species was shown in parenthesis. Means (±S.E.) marked with different letters were significantly different from each other (P <0.05). SnL, snout length; HL, head length; TrL, trunk length; TaL, tail length; BH, body height; BW, body width; SL, standard length. PF, number of pectoral fin rays; AF, number of anal fin rays; DF, number of dorsal fin rays; TrR, number of trunk rings; TaR, number of tail rings. * The data are for the holotype of H. casscsio sp. nov.

Principal components SnL, snout length; HL, head length; TrL, trunk length; TaL, tail length; BH, body height; BW, body width; SL, standard length. PF, number of pectoral fin rays; DF, number of dorsal fin rays; TrR, number of trunk rings; TaR, number of tail rings.

Molecular analysis. All cyt b sequences were trimmed to a consensus length of 809 bp. A total of 30 unique cyt b haplotypes were generated from all specimens, and three haplotypes were observed among the new species. Eighteen CR haplotypes were observed among the specimens of H. casscsio sp. nov. The NJ tree showed that all of the individuals of the same species cluster together ( Fig. 3 a, b). No haplotype was shared between species in our data set. Although H. casscsio sp. nov. was morphologically similar to H. mohnikei (interspecific distance: 16.1%), there was a closer genetic relationship between H. casscsio sp. nov. and H. kuda (interspecific distance: 2.4%) ( Fig. 3 a and Table 3 ). The two species formed a sister group with a strongly significant bootstrap value of 100% ( Fig. 3 ).

Etymology. The name is derived from the abbreviation of ‘South China Sea Institute of Oceanology, Chinese Academy of Sciences’.

Distribution. Hippocampus casscsio sp. nov. appears to be relatively limited to the Beibu Bay (Beihai, Fangchenggang, Lingao, Dongfang, Sanya and Lingshui), China ( Fig. 4 ).

Figures

FIGURE 1. Holotype of Hippocampus casscsio sp. nov. (SCSMBC 007414, SL 90.5 mm, male).

FIGURE 2. Comparison of morphological characteristics and body sizes among the three seahorses H. kuda, H. casscsio sp. nov., and H. mohinikei (a), and the principal components analysis (PCA) of the three species according to the morphological data (b).

FIGURE 3. Neighbor-joining (NJ) trees based on cyt b (a) and CR (b) from seahorses haplotypes of Hippocampus along China’s coast.

FIGURE 4. Map generated by Surfer ® for Windows (Keckler, 1997) showing the sampling locations for the specimen of new seahorse species, H. casscsio sp. nov., along China’s coast. Holotype location indicated by triangle.

Tables

TABLE 1. Morphological characteristics of three seahorses H. casscsio sp. nov., H. kuda and H. mohnikei.

	Holotype*	H. casscsio sp. nov. (16)	H. kuda (11)	H. mohnikei (16)
Morphometrics
SnL	4.5	5.4	15.3±0.64	2.4±0.53
HL	15.0	17.9±2.15	34.5±1.86	10.5±1.23
TrL	24.5	32.1±5.86	49.9±2.55	19.2±1.84
TaL	51.0	63.9±10.00	86.1±5.89	36.7±4.69
SL	90.5	113.9±14.07	170.5±9.97	66.4±7.11
BH	75.5	96.0±12.52	86.1±5.89	55.8±5.98
BW	14.0	17.1±2.92	21.2±2.52	8.7±1.24
SnL/HL	0.30	0.3±0.04b	0.4±0.01a	0.2±0.03c
TrL/SL	0.27	0.3±0.04a	0.3±0.01a	0.3±0.02a
	0.56	0.6±0.04a	0.5±0.01b	0.6±0.02a
HL/SL	0.17	0.2±0.01a	0.2±0.00a	0.2±0.01a
Meristics
PF	15	15	16	13
DF	16	16	17	16
AF	4	4	4	4
TrR	10	10	11	11
TaR	35	35(33–37)	36(36–38)	38(37–40)

TABLE 2. Loadings of components matrix and contributions of each axis to total variance.

	1	2
HL	0.974	0.200
SnL	0.950	0.289
TrL	0.976	0.068
TaL	0.973	-0.089
BH	0.994	-0.030
SL	0.997	0.022
BW	0.947	-0.210
PF	0.941	-0.214
DF	0.837	0.517
TrR	-0.075	0.961
TaR	-0.521	0.770
Variance (%)	77.174	18.290